1. Field of the Invention
The present invention relates to a linear guide, and more particularly, to a separator (partition element), a linear guide equipped with the separator, and an apparatus using the linear guide.
The present invention also relates to a direct-acting apparatus used in industrial machinery; e.g., a linear guide bearing, a ball screw, a ball spline, and a linear ball bush.
2. Description of the Related Art
A linear guide using roller-shaped rolling elements as rolling elements comprises a guide rail for guiding an object which moves linearly; and a slider disposed on the guide rail in a movable manner. When the slider has moved over the guide rail in a longitudinal direction thereof, a plurality of roller-shaped rolling elements incorporated in the slider roll in the longitudinal direction of the guide rail between a raceway formed on the guide rail and another raceway formed on the slider.
Such a linear guide has greater rigidity and load capacity than a linear guide using spherical rolling elements. When adjacent rolling elements come into contact with each other, at the area of contact the respective rolling elements rotate in opposite directions. Therefore, the frictional force which develops at the contact area hinders smooth rolling actions of the rolling elements. In the previously-described linear guide, axial fluctuations; that is, so-called skews, arise in the rolling elements, which may in turn impair the operability of the linear guide.
To solve the problem, JP-A-2001-132745 and JP-B-40-24405, which are provided below, disclose a linear guide which has separators sandwiched between roller-shaped rolling elements, to thereby prevent occurrence of contact between rolling elements and skew.
However, the linear guide disclosed by JP-A-2001-132745 uses, as separators to be interposed between the roller-shaped rolling elements, a separator main body which has, on both sides in the front and rear direction thereof, recessed surfaces to contact a circumferential surface of the roller-shaped rolling element; and a flange section which extends from either side of the separator main body in opposite directions and comes into surface contact with one end face of a rolling element. Therefore, the rotational resistance of the rolling element is increased on one end of the separator main body, thereby decreasing the rotational balance of the rolling elements. Therefore, the effect of suppressing skew is insufficient.
The linear guide disclosed by JP-B-40-24405 employs a configuration wherein partition elements, in which plate-like webs extending toward centers of rolling elements are provided on both sides of each partition element, are used as separators; and wherein the webs of the partition elements are brought into contact with each other in the vicinity of the center of the rolling elements, thereby supporting each other. Therefore, a clearance rises between any of adjacent rolling elements and any one of adjacent partition elements. As a result, a distance between the centers of two rolling elements which are adjacent to each other with a partition element interposed therebetween become larger than necessary. Therefore, the number of rolling elements disposed in a load zone may be decreased, which may in turn result in a decrease in load capacity. Moreover., in the case of the linear guide described in JP-B-40-24405, the widthwise length of the partition is greater than the axial length of the rolling element. Hence, a clearance arises between the end face of the rolling element and the web. Thus, an effect for inhibiting occurrence of skew is insufficient.
In a linear guide having a plurality of rolling elements arranged therein, the rolling elements circulate endlessly, and the respective rolling elements roll in a single direction. When adjacent rolling elements come into contact with each other, at the area of contact the respective rolling elements rotate in opposite directions. Therefore, the force—which develops at the contact area and presses the rolling elements—hinders smooth rolling actions of the rolling elements which remain in contact with each other. This may impair smooth operation of the linear guide.
When columnar or cylindrical rollers are employed for rolling elements, the rigidity and load capacity (allowable bearing load) of the rolling elements can be enhanced as compared with a case where spherical balls are adopted as rolling elements. However, axial fluctuations; that is, so-called skews (a phenomenon of longitudinal axes of columnar or cylindrical rollers failing to remain orthogonal to the traveling direction and becoming skewed), arise in traveling rollers, which may in turn impair the operability of the rolling elements and, by extension, the operability of the linear guide.
For this reason, the linear guide is constructed to prevent the rolling elements from coming into direct contact with each other by means of interposing separators (partition elements) between rolling elements, in an attempt to make rolling (traveling) actions of the rolling elements smooth, enhance the operability of the same, and reduce noise which arises during traveling of the rolling elements.
For instance, JP-B-40-24405, JP-UM-A-52-110246, and JP-B-56-2206 provided below describe separators to be interposed between rollers.
JP-B-40-24405 discloses partition elements as partition elements (separators) to be employed in a bearing using rollers. The partition element has a recessed contact section fitting to a cylindrical surface of the roller, and arm sections (webs) which are provided on respective sides of the partition element with the center thereof aligned therebetween in the direction of linear motion and are extended to the center of the roller. This partition element is configured to bring the arm sections thereof into contact with arm sections extending from adjacent partition elements.
However, the partition element disclosed by JP-B-40-24405 is configured to transmit the force—which is transmitted to the partition element when the roller rolls and moves—to the next partition element by way of an arm section provided on the next partition element. In reality, the partition element suffers the following problems.
As motion of the roller shifts from a linear section to a change direction section, a change arises in the areas where the arm sections come into contact with each other, which may in turn widen a distance between rollers originally, in order to increase load capacity of the linear guide, rollers and partition elements are arranged comparatively tightly within the change direction section so that the largest possible number of rollers can be arranged in a load zone. For this reason, by means of action of the widening force, force which is greater than necessary may act on the arm sections remaining in contact with each other, thereby hindering smooth movement of the rollers and partition elements and deteriorating operability.
As described in JP-B-40-24405, in the case of the partition elements which transmit force by means of bringing arm sections into contact with each other, a gap arises between a roller and a partition element located before or after the roller in the traveling direction, which may fail to sufficiently hinder occurrence of skew. Moreover, the number of rollers which can be disposed in the load zone is diminished by presence of the gap. This may also result in a failure to sufficiently enhance the load capacity.
In a linear guide, a slider moves relative to a guide rail while a plurality of rolling elements are rolling through an endless circulation path. When the slider has moved relative to the guide rail, the respective rolling elements move while rolling in one direction, and hence adjacent rolling elements contact each other. As a result, there arises the problems of hindrance of smooth rolling actions of the rolling elements, rapid progress in abrasion of the rolling elements, and an increase in noise.
Therefore, there has hitherto been known a linear guide which smoothly rolls rolling elements to thus prevent early abrasion of the rolling elements and is provided with separators interposed between adjacent rolling elements in order to activate the linear guide while suppressing emission of noise (see, e.g., JP-A-11-247855, JP-A-2000-291668, JP-A-2001-317552, JP-A-2002-089651, JP-A-2002-039175 and JP-A-2002-156018).
A known conventional separator has arm sections or the like for retaining adjacent rolling elements in a predetermined position. For instance, according to the technique described in JP-A-11-247855, a train of rolling elements is constituted by connecting adjacent separators with rolling elements sandwiched therebetween. The rolling elements can be aligned in parallel within the endless circulation path by means of interconnecting the separators. As a result, axial fluctuations (skew) in and interference between the rolling elements is lessened, thereby enabling stable circulation of the rolling elements.
According to techniques described in, e.g., JP-A-2000-291668, JP-A-2001-317552, JP-A-2002-7089651, JP-A-2002-039175 and JP-A-2002-156018, a lubricant reservoir section, which is formed from a recess or a through hole, is formed in the separator for preserving lubricant. As a result of the lubricant reservoir section being formed in the separator, the rolling elements are smoothly rolled, thereby activating the linear guide while preventing early abrasion of the rolling elements and generation of noise.
However, according to the technique described in JP-A-11-247855, the separator is not provided with a recess, a through hole, or the like which is employed for preserving lubricant according to the techniques described in JP-A-2000-291668, JP-A-2001-317552, JP-A-2002-089651, JP-A-2002-039175 and JP-A-2002-156018. Therefore, the technique allows some improvements in terms of smooth rolling action of the rolling elements, prevention of early abrasion of the rolling elements, and activation of the linear guide while suppressing generation of noise.
In the meantime, according to the techniques described in JP-A-2000-291668, JP-A-2001-317552, JP-A-2002-089651, JP-A-2002-039175 and JP-A-2002-156018, the separator is not equipped with arm sections or the like which are employed for actively regulating the position of the rolling elements according to the technique of JP-A-11-247855. Therefore, a problem of stable circulation of the rolling elements while effectively suppressing axial fluctuations (skew) in and interference between the rolling elements still remains unsolved.
The present inventors have worked on development of a separator capable of comprehensively solving the above-described problems.
An assembly operation for manually inserting rolling elements into an endless circulation path while interposing separators between adjacent rolling elements is very time consuming. Therefore, automation of the assembly operation is desirable in terms of an improvement in productivity.
Therefore, a conceivable method is to align the separators through use of an automatic alignment machine, such as a parts feeder, and to successively automate the assembly operation through use of, e.g., a robot.
As separators capable of comprehensively solving the foregoing problems, there were prepared a plurality of separators which merely constitute a train of rolling elements, each rolling element having arm sections enabling alignment of the rolling element, and a lubricant reservoir section constituted of a recess or a through hole. A test was performed for automatically aligning the separators. In some cases the arm sections came to fit into the through holes or the like serving as the lubricant reservoir sections, which resulted in entanglement of the separators and ended in failure to align the separators.
As mentioned above, there still remain problems to be solved before realizing separators which have the function of controlling the position of the rolling elements and storing lubricant and take into consideration automation of production.
As shown in, e.g., FIG. 40, a linear guide bearing apparatus having an axially-extending guide rail 501 and a slider 502 disposed so as to straddle the guide rail 501 and be relatively movable in an axial direction has been known as a conventional direct-acting apparatus of this type.
Two axially-extending raceway surfaces 503 are formed on either side surface of the guide rail 501 in a transverse direction thereof, and hence a total of four raceway surfaces 503 are formed. Raceway surfaces 505 opposing the raceway surfaces 503 are formed on each inner side surface of a sleeve section 504 of a slider main body 502A of the slider 502.
A plurality of cylindrical rollers 506, serving as rolling elements, are rotatively loaded between the raceway surfaces. The slider 502 can axially, relatively move over the guide rail 501 by means of rolling actions of the cylindrical rollers 506.
As the slider 502 moves, the cylindrical rollers 506 interposed between the guide rail 501 and the slider 502 rotate and move toward an axial end of the slider 502. However, in order to continuously move the slider 502 in the axial direction, the cylindrical rollers 506 must be circulated endlessly.
Holes 507 are formed in the sleeve section 504 of the slider main body 502A so as to penetrate through the sleeve section 504. A circulation tube 8 whose inside is formed into a passage (rolling element passage) 508a for the cylindrical rollers 506 is fitted into each of the holes 507. A pair of end caps 509, which serve as rolling element circulation components, are fixed to the respective axial ends of the slider main body 502A through use of screws or the like. A change direction path 510 (see FIG. 41B)—which brings the raceway surfaces 503, 505 into communication with the rolling element passage 508a and is formed into a semi-circular shape—is formed in each of the end caps 509, thereby forming an endless circulation path for the cylindrical rollers 506.
The plurality of cylindrical rollers 506 that circulate the endless-circulation path rotate about roller shafts in one direction. When adjacent cylindrical rollers 506 have come into contact with each other, velocities of the rollers at that contact area are oriented in opposite directions. Force stemming from the contact hinders smooth rolling action of the cylindrical rollers 506.
As shown in FIG. 41., with this being the case, separators (partition elements) 520 are interposed between adjacent cylindrical rollers 506, thereby hindering the cylindrical rollers 506 from coming into direct contact with each other. As a result, the travel of the slider 502 is made smooth, and an attempt is made to diminish noise which arises during the course of travel of the slider. As shown in FIGS. 42 through 44, the separator 520 comprises a separator main body 521 interposed between the adjacent cylindrical rollers 506, and arm sections 522 which are arranged such that the axial end faces of the cylindrical roller 506 are sandwiched between the arm sections 522 and which are formed integrally with the separator main body 521. Recessed sections 521a agreeing with the outer circumferential shape of the cylindrical roller 506 are formed in areas of the separator main body 521 opposing the outer circumferential surface of the cylindrical roller 506. In FIG. 40, reference numeral 523 designates a separator guide member interposed between an outer side surface of the guide rail 501 and the inner side surface of the slider 502.
When the cylindrical rollers 506 circulate through the space defined between the raceway surfaces 503 and 505, the change direction path 510, and the rolling element passage 508a, the arm sections 522 of the separators 520 are guided along guide grooves 524 in the direction in which the cylindrical rollers 506 are circulated, wherein the guide grooves are formed in the separator guide member 523, the rolling element passage 508a, and the change direction path 510.
Incidentally, the present applicants have already proposed use of an elastomeric material, such as Hytrel® or Pelprene® (manufactured by Toyobo Co., Ltd. under this tradename), in order to absorb fluctuations in the length of a path due to a change in the phase of the rolling element in the endless circulation path for the rolling elements (see JP-A-2002-21849). Further, the separators have been swollen by fat and oil of lubricant or the like. Depending on a contact position between the rolling element and the separator, the pitch between the rolling elements may have become greatly changed, thereby raising a problem which adversely affects operability, a low noise characteristic, and durability. Therefore, the contact position between the rolling element and the separator is defined as a position of 50% or less the diameter of the rolling element, particularly a position ranging from 30% to 50% (when the positions are converted into contact angles, a position where a contact angle of 30° or less is achieved, particularly a position where a contact angle of 17.5° to 30° is achieved) (see JP-A-2003-49834).
However, depending on a radius curvature “f” of the recessed section of the separator {determined by (a radius R of a groove of a recessed section)/(a radius Dw of a rolling element)} or the value of a thickness 2δ of the bottom of the groove of the recessed section of the separator, the contact position between the rolling element and the separator defined in JP-A-2002-21849 cannot always attain an optimum value. For instance, when there are employed 0.54 for the curvature radius “f” of the recessed section of the separator; 8 mm for the radius Dw of the rolling element; and 1.2 mm (a value which ensures the number of rolling elements required to satisfy load capacity or the like) for the thickness 2δ of the recessed section of the separator, the contact position between the rolling element and the separator exceeds 50% (corresponding to a contact angle of 30°) of the diameter of the rolling element, and 52% (corresponding to a contact angle of 31°) becomes an optimum value {a dimensional difference between the length of the swelling in the separator in a radial direction thereof and the thickness of the swelling in the separator in a thicknesswise direction thereof becomes zero (see FIG. 45); the swelling in the radial direction leads to a decrease in the pitch between the rolling elements, and the swelling in the thicknesswise direction leads to an increase in the pitch between the rolling elements}.